1. Field of the Invention
The present invention relates to a method for determining a production parameter in the case of injection molding of resin, a method for producing an injection molding using the production parameter, an injection molding device, and a program.
2. Related Background Art
When molding resin with an injection molding device, there is a demand to minimize the mold clamping force necessary for molding. Normally, the mold clamping force of a device is predetermined by using a safety factor allowance as well as the mold clamping force required for molding, therefore the smaller the required mold clamping force for molding, the less the output of the pressure generating system in a injection molding device is required. Accordingly, if the device can be substituted for a smaller one, the running cost decreases, and this is the reason why there is such a demand to minimize mold clamping force. Furthermore, even in the case of the identical device, the smaller the mold clamping force required, the more gives the higher advantages such as electric power saving and protection of molds are obtained due to the reduced predetermined mold clamping force.
As the mold clamping force is expressed by [(the resin pressure in the cavity)×(the projected area)], reduction of the minimum mold clamping force required for molding (the maximum mold clamping force) is achieved by controlling either or both of these factors. The resin pressure in the cavity varies with parameters of fluidity of the resin to be used, inflow speed, temperature, pressure loss along the injection conduit including a runner, and so on. For stable molding of a resin product, however, an optimum range is predetermined for the respective parameters, and these parameters should be adjusted within the respective limited ranges. On the other hand, the projected area is determined necessarily in principle, once the shape of a resin product is fixed. Nevertheless, the projected area can be substantially decreased subject to the shape of the resin product.
For example, Japanese Patent Laid-open Gazette No. 2002-355866, page 2 discloses, in the case where the product shape extends in a longitudinal direction, that a plurality of gates through which molten resin is injected into the cavity are arranged along the direction from the resin filling starting side to the filling completion side, and the molten resin is sequentially injected into the cavity at a specified interval starting with the injection at the filling starting gate, thus the resin injected in early stage comes to an almost cooled and solidified state when reached the final filling stage, whereby the substantial projected area which should be filled with the molten resin injected from the last gate is significantly reduced compared with the total projected area of the cavity.
In injection molding it is necessary to provide a plurality of gates depending on the dimensions and shape of the product. In use of a plurality of gates, weld will occur at a merging section of the molten resin injected from individual gates. In the weld line occurrence section, the product may suffer from determination of appearance and decrease in strength depending on the condition of merging of the molten resin. Accordingly, it is requested to shift the weld line to a position raising as few problems as possible regarding with appearance and strength.
For example, Japanese Patent Laid-open Gazette No. Heisei 8-118420, pages 2 to 3 describes the prevention of weld line occurrence by injecting a softened resin material from the second gate into the cavity at almost the same time or after the resin injected from the first gate passes over the second gate. Japanese Patent Laid-open Gazette No. 2001-277308, pages 7 to 9 discloses a technology to predict the location of weld lines generated in a molding through flow simulation of a molding process by dividing the shape of the molding into fine elements, further by adjusting the open or close of valve gates on the basis of thus predicted weld lines to shift the weld lines to a preferable corrected location.